Pump it up! Diesel injection pump tipsJune 5, 2018
A diesel differs from a gasoline engine because the cylinders are filled only with air during the intake stroke. The mixture of oxygen, nitrogen, and two percent other gasses is compressed until it reaches an extremely high temperature and pressure, at which point fuel is sprayed into the chamber. Spontaneous combustion occurs as a result of the hot compressed air and the fuel’s flash point. The expanding flame is used to drive the piston that transfers energy to the crankshaft.
The diesel fuel injection pump is critical to this process. It is responsible for pressurizing, metering, distributing and timing the fuel delivery to the engine under each load and rpm condition. Though the nozzle actually supplies the fuel to the cylinder bore, it is the injection pump that allows that to occur.
Injection pumps have proven to be very reliable but since it is the heart of the diesel, if anything is askew the engine will not run properly and can possibly become damaged. Thus, it is prudent for every farmer to have a cursory knowledge of injection pump operation and service requirements.
Varied approach… same goal
Within the agricultural equipment community, a variety of different diesel engines have been employed. Some companies produce their own engines (John Deere, Case/IH, New Holland, etc.) while others use those made by Cummins, Caterpillar or Detroit Diesel, to name a few. Regardless of the make an injection pump is part of the fuel system and can vary in style. There are two basic types of injection pumps found on farm engines. These are either an in-line or rotary distributor design.
The in-line pump is often referred to as a pump-line-nozzle (PLN) while the other popular design is a rotary distributor pump. In the late 1920s, the Bosch Corporation of Germany developed the in-line pump. The modern version is identified as a port-helix design. In 1941 in America, Vernon Roosa patented his design for a rotary (round) distributor injection pump. It was embraced by the industry and marketed by different manufacturers such as Ambac PSB/PSJ (American Bosch), CAV, Lucas and Stanadyne.
Although the Roosa rotary injection pump was not the first it was easily the most successful and it generated many copycat designs. One of these is the American Bosch VE. It lasted into the 1990s and was employed on light-duty diesel engines and can be found in smaller tractors and other equipment such as a skid-steer loader. The Bosch VE is a hydro-mechanical sleeve metering distributor pump that employs a single plunger-pumping element while the Roosa is an inlet-metering, opposed plunger style.
The Stanadyne DB2 formerly marketed as a Roosa-Master design or some variation on it, is commonly found on many farm-based diesel engines. Its simple theory meant a low initial cost and less to go wrong in the field.
Other injection pumps can be found on farm equipment such as the Detroit Diesel design, Caterpillar style, and the Cummins PT. The service information in this primer will apply to all injection pumps but each will have application specific procedures that should be referenced in the appropriate shop manual.
A brief overview
The DB2 is an opposed-plunger, inlet metering (the Bosch VE is a sleeve metering design) distributor-type injection pump. It was designed for low cost production and simplicity. A typical DB2 (there were slight variations on the design for different engines) has a total of approximately 100 components and only four main rotating members.
Fuel is drawn from the fuel tank by a mechanical lift pump that is independent of the DB2 injection pump and passes through filters and then into the injection pump inlet. The fuel then flows past the inlet filter screen to the vane-operated transfer pump contained in the pump end cap. The vane-type transfer pump consists of a stationary liner and spring-loaded blades carried in slots at the rear of the transfer pump rotor. As the blades rotate in the liner they move outward and the volume increases until the leading blade passes out of registry with the inlet slot. The fuel between the blades is carried to the bottom of the transfer pump liner and enters the outlet groove. As a result, pressurized fuel is delivered through the pump into a channel to the hydraulic head passage.
The pressure regulator assembly in the transfer pump regulates fuel volume based on changes in pump speed — pressure increases with pump speed.
The advance system is a simple, direct-acting hydraulic mechanism. Powered by fuel pressure from the transfer pump the advance mechanism moves the power piston to rotate the cam to vary the delivery timing. It advances or retards the start of fuel delivery in response to engine speed changes. When engine speed decreases hydraulic pressure is reduced and the cam retards because of low transfer pressure. When engine speed increases so does the pump pressure and this moves the advance piston and cam.
The min-max governor regulates the injection pump at low idle and maximum rated speed. At speeds between these two ranges the throttle lever and governor spring directly control the metering valve.
A typical port-helix in-line pump is flanged mounted and is driven one complete rotation for a complete engine cycle (720 crankshaft degrees) (It is the same drive ratio as a rotary design). It is crankshaft driven via timed reduction gears. The pump has an internal shaft that is made with eccentrics (lobes) designed to react against elements, one for each engine cylinder.
This style of pump includes a pump housing, cam box, camshaft (eccentric) tappets, barrel, plunger, rack and control valves and delivery valves. It can be considered a small engine. It is an excellent design but is more complex than the rotary distributor pump. Even with its complexity, industry statistics state that a majority of port-helix pumps that are removed from a farm engine have nothing wrong with them and are misdiagnosed.
The intent of this overview is to establish that both pump designs are very complex. Thus, dirt and the lack of lubrication in the fuel become real issues along with common wear parts.
As was stated in the nozzle primer, a majority of pump wear issues are due to excessive contaminants in the fuel such as dirt, grit and moisture, along with the lack of lubricity that is part of modern diesel fuel. Lubrication is not as much of a concern with an electronic diesel since there is no injection pump and the nozzles are controlled though a microprocessor in similar fashion as a gasoline engine. For this reason, the most effective maintenance that can be done on the farm is to supply the injection pump with clean and lubricity-enhanced diesel fuel. This small step goes a long way in eliminating costly problems and downtime when you need to be in the field and not in the shop.
Other factors also come into play when a port-helix pump is employed. A rotary distributor pump is lubricated by diesel fuel. An in-line style has a supply of engine oil fed to it. Poor quality engine oil and maintenance along with the lack of sulfur in the diesel fuel can spell disaster for an injection pump of this style.
The lower portion of the port-helix pump is lubricated by engine oil. Some older designs had the lubrication circuit for the pump separate from the engine and the level of lubricant would need to be checked and filled through a dipstick on the pump cam box. For the last many years, the lubricant for the pump is usually from the engine.
The diesel fuel being pumped through the charging gallery lubricates the upper portion of the in-line injection pump. The lubricity of the fuel is critical to upper pump life.
It is imperative that the diesel fuel and the lubricating oil in the injection pump do not mingle for the sake of both the pump and the engine. Any minute leakage can lead to viscosity break down of the engine oil and damage the pump and engine parts. If an analysis of the crankcase lubricant shows excessive fuel contamination, a poor viscous seal in the port-helix injection pump often is the cause. This (fuel contamination) can cause excessive engine bearing; piston ring and cylinder wall wear due to a lack of lubricity from the fuel in the oil.
For the best performance from the engine there is a need to service any injection pump and have it timed properly. Pump timing usually skews over a period of years with the engine using more fuel and loosing power. It happens slowly and you often do not notice it. For this reason, an older engine should have the pump periodically benched checked. Any parts that are worn can be replaced and the fuel delivery and timing confirmed. A relationship with a good pump and nozzle shop in your area along with the proper fuel lubricity and engine oil service will mean that your equipment will stay working in the field for many years to come!